Refractive and anatomic accuracy vital with accommodating IOLs

Surgeons must directly address the corneal astigmatism by adjusting incisional methods.

Issue: September 25, 2008

ByUday Devgan, MD

The ideal IOL implant would be similar to a young, natural crystalline lens and provide sharp vision over a wide range, with great image quality and no dysphotopsias. There are currently no man-made body parts, whether IOLs, heart valves or artificial hips, that perform as well as young, healthy human parts — but we are getting closer every year.

Uday Devgan

The only accommodating IOL that is currently U.S. Food and Drug Administration-approved is the Crystalens (Bausch & Lomb); however, other products are in development that will soon enter the marketplace, including the Synchrony (Visiogen) and the Tetraflex (Lenstec). Simply inserting these IOLs at the time of cataract surgery is not enough. To maximize the visual results for our patients, we must achieve refractive and anatomic accuracy.

Refractive considerations

With the advent of optical methods to measure the axial length, such as partial coherence interferometry, the percentage of patients achieving an accurate postop refractive status (goal ±0.5 D) has increased, but this is for the spherical equivalent only. To maximize the patient’s visual results, we must address the corneal astigmatism to ensure that it is about 0.5 D or less for most cases.

In the future, we may have toric accommodating IOL designs, but for the near future, we need to directly address the corneal astigmatism by adjusting incisional methods. For small degrees of corneal astigmatism, 0.75 D or less, we can modulate the astigmatism by varying the placement of our clear corneal phaco incision. Because most sub-3-mm clear corneal phaco incisions cause a flattening of about 0.5 D, we can place this incision on the steep axis of the cornea to address the astigmatism.

For more significant degrees of astigmatism (1 D or more), the use of limbal relaxing incisions is recommended (Figure 1). A key consideration when making the limbal relaxing incision is additive effects of your clear corneal incision. If the patient has 1 D of corneal astigmatism at 90° and a clear corneal incision, which causes 0.5 D of flattening, is made at 180°, then the patient may need 1.5 D of limbal relaxing incisions at the 90° meridian.

Figure 1: A limbal relaxing incision is created at the 90° meridian by using a diamond blade

A limbal relaxing incision is created at the 90° meridian by using a diamond blade. The fixation ring provides stability of the globe and is marked in clock hours (30° segments) to provide a guide for incision length. The steel footplate of the diamond blade glides along the fixation ring to produce smooth, accurate incisions.

Images: Devgan U

Figure 2: The dashed red line indicates a 6.5-mm capsulorrhexis, which allows the 5-mm optic and the IOL hinges to be unobstructed

The dashed red line indicates a 6.5-mm capsulorrhexis, which allows the 5-mm optic and the IOL hinges to be unobstructed. The blue-outlined boxes are the paracentesis incision and the clear corneal main incision, which are both constructed to minimize their effect on corneal curvature. The green lines highlight the limbal relaxing incisions, which are used to treat the with-the-rule astigmatism, with the purple conjunctival ink marks indicating the 90° meridian.

With the postop goal of plano achieved, with minimal corneal astigmatism, the patient will recover sharp distance vision. The near vision, however, is often a function of the anatomic positioning of the IOL in the eye.

Anatomic considerations

The accommodating IOLs are designed to move, flex, arch and/or change curvature in response to the accommodative effort of the ciliary muscles. This requires the lens to be securely positioned but not restricted by the capsular bag. Because of fibrosis, the capsular bag tends to contract and shrink-wrap the IOL, which may decrease the level of near vision that the patients recover.

In a single-focus IOL, we want the anterior capsular rim to cover the edge of the optic to securely hold it within the capsular bag. For the currently available accommodating IOLs, I prefer to have a capsulorrhexis that is significantly larger than the IOL optic so that the maximum range of accommodation can be achieved. For the Crystalens HD, which is touted to have more accommodative amplitude than the Crystalens, I prefer at least a 6-mm capsulorrhexis to allow freedom of the 5-mm optic. A slightly larger capsulorrhexis, which allows the IOL hinges more mobility, may prove to be of benefit (Figure 2).

Intraoperatively, the IOL should be placed so that it is vaulted posterior in order to have accurate IOL calculations because the effective lens position largely determines this. In addition, it is thought that the best visual results and accommodative amplitude are achieved with this lens positioning. If the anterior chamber deflates at the end of the case, simply re-inflating it with balanced salt solution is not enough. Re-position the IOL so that the haptic footplates are at the capsular bag equator and the optic is vaulted posterior. To keep the IOL in this position, it is imperative that incisions are completely water-tight at the end of the surgery.

With anatomic and refractive accuracy, the results can be remarkable, such as with the patient shown in these figures achieving 20/20 distance vision and J2 near vision the day after surgery. I expect that in the years to come, our technology will progress further, and although we may never find the fountain of youth, we will certainly achieve higher levels of accommodative reserve.

For more information:

Uday Devgan, MD, FACS, is in private practice at Devgan Eye Surgery in Los Angeles, Beverly Hills, and Newport Beach, California. Dr. Devgan is Chief of Ophthalmology at Olive View UCLA Medical Center and an Associate Clinical Professor at the Jules Stein Eye Institute at the UCLA School of Medicine. Dr. Devgan can be reached at 11600 Wilshire Blvd., Suite 200, Los Angeles, CA 90025; 800-337-1969; fax: 310-388-3028; e-mail: devgan@gmail.com; Web site: www.DevganEye.com. Dr.Devgan is a consultant to Abbott Medical Optics and Bausch & Lomb, and is a stockholder in Alcon Laboratories and formerly in Advanced Medical Optics. While.Dr. Devgan is a consultant to Bausch & Lomb Surgical and the Storz Instruments subsidiary, he has no direct financial interests in the products mentioned.

Reference:

Nichamin LD. Astigmatism control. Ophthalmol Clin North Am. 2006;19(4):485-493.